1. Technical Field
The present invention relates to a speaker, and more particularly to a speaker which may be slim and have a reduced thickness.
2. Background Art
In recent years, since high-definition televisions, wide-screen televisions, and the like are widespread, horizontally elongated television screens are becoming common. Further, since living spaces are relatively small in Japan, television sets are required to have reduced widths and thicknesses as a whole.
In general, speaker units (hereinafter, simply referred to as speakers) for use in a television are mounted lateral to both sides of its cathode-ray tube, and this is a cause of increasing the horizontal width of a television set. Therefore, conventionally, speakers having elongated structures such as rectangle-shaped structures and ellipse-shaped structures are used as speakers for televisions. Further, since cathode-ray tubes have become horizontally elongated, it is necessary to increase reduction of the horizontal widths of speakers. Simultaneously, a speaker is required to output an enhanced quality of sound and voice so as to correspond to a screen which enables an enhanced quality of image to be displayed. In addition, since thin-screen televisions for which plasma displays or liquid crystal displays are used become widespread, speakers are required to become slimmer and have further reduced thicknesses.
A conventional elongated (slim-type) speaker will be described. FIG. 37 is a diagram illustrating a configuration of a conventional slim-type speaker 900. FIG. 37(a) is a plan view of the conventional slim-type speaker 900. FIG. 37(b) is a cross-sectional view of the conventional slim-type speaker 900 in a long side direction (along c-c′). FIG. 37(c) is a cross-sectional view of the conventional slim-type speaker 900 in a short side direction (along o-o′). As shown in FIG. 37, the conventional slim-type speaker 900 includes a magnet 901, a plate 902, a yoke 903, a frame 904, a voice coil bobbin 905, a voice coil 906, a damper 907, a diaphragm 909, a dust cap 910, and an edge 911.
The voice coil 906 is a wound lead wire formed of copper, aluminum or the like, and is fixed to the voice coil bobbin 905 having a cylindrical shape. The voice coil bobbin 905 supports the voice coil 906 such that the voice coil 906 is disposed in a magnetic gap 908 formed by the magnet 901, the plate 902, and the yoke 903. Further, the voice coil bobbin 905 is connected to the frame 904 via the damper 907. Furthermore, the voice coil bobbin 905 is adhered to the diaphragm 909 having an ellipsoidal shape or an almost ellipsoidal shape, on a side opposite to a side on which the voice coil 906 is fixed thereto. The dust cap 910 having an almost semicircular cross section is fixed to the center portion of the diaphragm 909. The edge 911 has an annular shape, and has a semicircular cross section. Further, the inner periphery of the edge 911 is fixed to the outer periphery of the diaphragm 909. The outer periphery of the edge 911 is fixed to the frame 904.
When the conventional slim-type speaker 900 is driven, a drive current is applied to the voice coil 906. In this case, due to the drive current applied to the voice coil 906 and an effect of a magnetic field generated around the voice coil 906, the voice coil bobbin 905 performs piston movement. Thus, the diaphragm 909 vibrates in the direction in which the voice coil bobbin 905 performs the piston movement. As a result, a sound wave is emitted from the diaphragm 909. The conventional slim-type speaker 900 as shown in FIG. 37 is disclosed in, for example, Patent Document 1. FIG. 38 is a diagram illustrating a relationship between a reproduced-sound pressure level and a frequency characteristic, which is observed when 1 W of electric power is supplied to the conventional slim-type speaker 900. In FIG. 38, the vertical axis represents reproduced-sound pressure levels, and the horizontal axis represents drive frequencies. A microphone for measuring the reproduced-sound pressure levels as shown in FIG. 38 is disposed, on the central axis of the slim-type speaker 900, in front of the slim-type speaker 900 so as to be distant therefrom by 1 m.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-32659